Visual overview of optical transmitters
Often, familiar system administrators who have not previously encountered optical fiber have questions about how and what kind of equipment is needed to establish a connection. Having read a little, it becomes clear that an optical transceiver is needed. In this review article I will write the main characteristics of the optical modules for receiving / transmitting information, tell you the main points related to their use, and attach a lot of visual images with them. Carefully, under the cut a lot of traffic, I made a bunch of my own photos.
Today, virtually any network equipment for data transmission over Ethernet networks, which provides connectivity via optical fiber, has optical ports. They install optical modules into which fiber can already be connected. An optical transmitter (laser) and a receiver (photo sensor) are built into each module. In classical data transmission using them, it is supposed to use two optical fibers - one for reception, the other for transmission. The image below shows a switch with optical ports and installed modules.
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That's about these little electronic gizmos on and will be discussed.
Periodically there are questions about what kind of optical transceiver is needed in a particular situation. If there is a price list before our eyes, then they simply run up from the abundance of all kinds of items. I will try to clarify what the various letters and numbers mean in the names of the modules and which of them you may need. Optical modules differ in form factor (GBIC, SFP, X2 ...), type of technology ("direct", CWDM, WDM, DWDM ...), power (in dithebels), connectors (FC, LC, SC).
First of all, modules differ in their form factors. I will tell a little about various options.
GigaBit Interface Converter was actively used in the 2000s. The very first industrially standardized format of modules. Very often used for transmission over multimode fibers. Now almost not used because of its size. I still have one old tsiska 3500, still without CEF support, in which you can use these modules. In the image below are two GBIC modules 1000Base-LX and 1000Base-T:
Small Form-factor Pluggable, heir to GBIC. Probably the most common format to date, much more convenient because of the smaller size. This form factor has allowed to significantly increase the density of ports on the network equipment. Due to this size, it became possible to realize up to 52 optical ports on one piece of iron in one unit. Used to transfer data at speeds of 100Mbits, 1000Mbits. On the image below is a switch with optical ports and a pair of 1000Base-LX and 1000Base-T modules.
Enhanced Small Form-factor Pluggable. Have an identical SFP size. A similar size allowed the equipment to be made with ports that support regular SFP and SFP +. Such ports can operate in 1000Base / 10GBase modes. Only long-range CWDM modules are longer because of the radiator. Used to transfer data at speeds of 10 Gbits. Some features gave small dimensions - for long-range modules there are cases of excessive heating. Therefore, for the transfer of more than 80 km of such modules yet. In the picture below are two SFP + modules - CWDM and the usual 10GEBase-LR:
10 Gigabit Small Form Factor Pluggable. As well as SFP +, they are used to transfer data at speeds of 10 Gbits. But unlike previous ones, a little wider. The increased size allowed them to be used for shooting a long distance in comparison with SFP +. Below is an extra charge for Huawei with installed XFP and a couple of such modules.
Modules used primarily in Cisco hardware. Used to transfer data at speeds of 10 Gbits. Now it is already occasionally possible to find application for them, occasionally it is possible to meet in old lines of routers. Also, these modules are to connect the copper wire 10GBase-CX4. Unfortunately, I only had one XENPAK-module 10GEBase-LR and an old Cisco-WS-X6704-10GE board for them.
Further development of modules format XENPAK. Often, you can install a TwinGig module into the X2 connectors, into which you can already install two SFP modules ... This is necessary if there are no 1GE optical ports on the equipment. Basically, the X2 form factor uses Cisco. There are X2-SFP + (XENPACK-to-SFP +) adapters available. Interestingly, such a kit (adapter + SFP + module) is cheaper than one X2 module.
Unfortunately, I only had an adapter in my hands, but to understand how these modules look and what size they will be enough for. The figure below shows the X2-SFP + adapter with the SFP + module inserted.
But if anyone is interested, here you can see more pictures and features of this connector.
Yes, I did not touch on the relatively new form factors (QSFP, QSFP +, CFP). At the moment they are not very common.
As you know, the 802.3 committee has adopted many different Ethernet standards. Accordingly, optical modules support one of them. A nice cheat sheet for Ethernet standards is here . The following types are now common:
Of course, there are optical modules for other standards, including 40GE and 100GE. I have listed the main types used in provider networks. Usually in the name or specification it is written, according to what standard this or that module will work. But it is still important to see if this standard supports the equipment port where the module will be installed. For example, 100Base-LX will not start in a switch port that supports only 1000Base-LX. This feature must also be considered.
The optical modules described above transmit a signal mainly at a wavelength of 1310 nm or 1550 nm on two fibers (one for transmission, the other for reception). They have a broadband photodetector (take all) and a laser emitting at a certain wavelength (roughly of course). But it is possible to use wavelength compression. This makes it possible to use a smaller amount of fibers to organize several channels, thereby increasing the throughput of a single fiber.
Such modules work in pairs, on the one hand, the signal is transmitted at a wavelength of 1310 nm, on the other hand, 1550 nm. This allows instead of two fibers for the organization of one channel to use one. The receiver on such modules remains broadband. Happen both for 1GE, and for 10GE. Below is a photo of a pair of WDM modules with different connectors for connecting patch cords LC and SC.
In most cases, it is preferable to use WDM modules for short distances. Their price is not very big (1 thousand rubles per module versus 500 rubles per ordinary). The reason is that you save the whole fiber, then it will be possible to drive out another similar channel later. Although of course there are other ways to save fiber.
Further continuation of WDM technology. With its use you can achieve up to 8 duplex channels on a single fiber. For these purposes, CWDM multiplexers are used (passive devices with a prism inside, allowing to divide the signal according to colors with a step of 20 nm in the range from 1270 nm to 1610 nm). For this, special CWDM modules are also used, commonly called “color” in common people, they transmit a signal at a specific wavelength. At the same time, the receiver on them is broadband. In addition, such optical modules are often made for transmission over long distances (up to 160 km). The figure below shows a small set of CWDM-SFPs, where you can pick up 2GE on a single fiber using multiplexers.
As you can see, the bows are different for everyone. Depending on the wavelength, the module has its own coloring. Unfortunately, they are different for all manufacturers.
Here comes the concept of the optical budget . True, his calculation is beyond the scope of this article. In short, the more ports available, the more channels you can multiplex, the more attenuation there will be. In addition, different wavelengths give different attenuation per kilometer of the transmitted signal. And you need to consider the type of fiber ...
You can write a lot about methods of selecting such modules, about the intersection of wavelengths, about unwanted lengths, about ADD / DROP-modules. But this is a separate issue.
This is the place where you will connect the optical patchcord. On the optical modules, two types of connectors are currently being used — SC and LC. Rough and slang - large and small squares. It is clear that having a patchcord with a SC connector, you will not connect it to the LC connector. You need to either change the patchcord, or put the adapter adapter. In most cases, SFP modules have an LC connector, while X2 / XENPAK is a SC. Above, the images already had modules with different connectors.
Optical modules are active equipment; they consume electricity and generate heat. This should be considered when connecting equipment to an electrical outlet. Also, a switch filled with powerful modules to the outset may require additional cooling.
Do not forget that lasers are built into the optical modules, and some safety precautions must be observed with them. Of course, in most cases, they do not provide any threat due to weak power, but there have been cases; long-range, powerful 10GE modules can burn out the retina or leave a burn if you use your finger as an attenuator.
Modern optical modules have the DDM (Digital Diagnostics Monitoring) function - they have a number of sensors built in through which you can determine the current value of some parameters. It looks through the interface of the equipment in which the module is installed. The most important parameters for you are the current received power and temperature.
A number of network equipment manufacturers prohibit the use of third-party modules in their equipment. At least before Cisco did not let them run, they simply did not work in it. Now, in narrow circles, teams are known that open up the possibility of using third-party devices, and Cisco has become less sensitive to this issue. However, if you wish, you can reflash any modules, there are special programmers on sale.
The port on the equipment (in most cases) lights up if a signal of sufficient power arrives at the module. If you connect two two-fiber modules with a single patchcord (just reception with transmission), on the one hand the port will light up, but nothing will work.
Yes, power may not only be weak. If the signal comes too strong, you can burn the photodetector. This usually refers to long-range power modules with a distance of> 80 km. To reduce power use special attenuators. Although if you do in the laboratory, you can simply wind a couple of coils of the patchcord on any pen or pencil.
Well that's all. The information presented here is enough to not get lost when choosing the module you need. It is important not to forget the main characteristics:
If someone interested in the topic, I advise you to look at the following:
What and why
Today, virtually any network equipment for data transmission over Ethernet networks, which provides connectivity via optical fiber, has optical ports. They install optical modules into which fiber can already be connected. An optical transmitter (laser) and a receiver (photo sensor) are built into each module. In classical data transmission using them, it is supposed to use two optical fibers - one for reception, the other for transmission. The image below shows a switch with optical ports and installed modules.
')
That's about these little electronic gizmos on and will be discussed.
Types of optical modules
Periodically there are questions about what kind of optical transceiver is needed in a particular situation. If there is a price list before our eyes, then they simply run up from the abundance of all kinds of items. I will try to clarify what the various letters and numbers mean in the names of the modules and which of them you may need. Optical modules differ in form factor (GBIC, SFP, X2 ...), type of technology ("direct", CWDM, WDM, DWDM ...), power (in dithebels), connectors (FC, LC, SC).
Various form factors
First of all, modules differ in their form factors. I will tell a little about various options.
GBIC
GigaBit Interface Converter was actively used in the 2000s. The very first industrially standardized format of modules. Very often used for transmission over multimode fibers. Now almost not used because of its size. I still have one old tsiska 3500, still without CEF support, in which you can use these modules. In the image below are two GBIC modules 1000Base-LX and 1000Base-T:
SFP
Small Form-factor Pluggable, heir to GBIC. Probably the most common format to date, much more convenient because of the smaller size. This form factor has allowed to significantly increase the density of ports on the network equipment. Due to this size, it became possible to realize up to 52 optical ports on one piece of iron in one unit. Used to transfer data at speeds of 100Mbits, 1000Mbits. On the image below is a switch with optical ports and a pair of 1000Base-LX and 1000Base-T modules.
SFP +
Enhanced Small Form-factor Pluggable. Have an identical SFP size. A similar size allowed the equipment to be made with ports that support regular SFP and SFP +. Such ports can operate in 1000Base / 10GBase modes. Only long-range CWDM modules are longer because of the radiator. Used to transfer data at speeds of 10 Gbits. Some features gave small dimensions - for long-range modules there are cases of excessive heating. Therefore, for the transfer of more than 80 km of such modules yet. In the picture below are two SFP + modules - CWDM and the usual 10GEBase-LR:
XFP
10 Gigabit Small Form Factor Pluggable. As well as SFP +, they are used to transfer data at speeds of 10 Gbits. But unlike previous ones, a little wider. The increased size allowed them to be used for shooting a long distance in comparison with SFP +. Below is an extra charge for Huawei with installed XFP and a couple of such modules.
XENPAK
Modules used primarily in Cisco hardware. Used to transfer data at speeds of 10 Gbits. Now it is already occasionally possible to find application for them, occasionally it is possible to meet in old lines of routers. Also, these modules are to connect the copper wire 10GBase-CX4. Unfortunately, I only had one XENPAK-module 10GEBase-LR and an old Cisco-WS-X6704-10GE board for them.
X2
Further development of modules format XENPAK. Often, you can install a TwinGig module into the X2 connectors, into which you can already install two SFP modules ... This is necessary if there are no 1GE optical ports on the equipment. Basically, the X2 form factor uses Cisco. There are X2-SFP + (XENPACK-to-SFP +) adapters available. Interestingly, such a kit (adapter + SFP + module) is cheaper than one X2 module.
Unfortunately, I only had an adapter in my hands, but to understand how these modules look and what size they will be enough for. The figure below shows the X2-SFP + adapter with the SFP + module inserted.
But if anyone is interested, here you can see more pictures and features of this connector.
Yes, I did not touch on the relatively new form factors (QSFP, QSFP +, CFP). At the moment they are not very common.
Different standards
As you know, the 802.3 committee has adopted many different Ethernet standards. Accordingly, optical modules support one of them. A nice cheat sheet for Ethernet standards is here . The following types are now common:
- 100Base-LX - 100 megabits per fiber per 10km
- 100Base-T - 100 megabits of copper per 100 m
- 1000Base-LX - 1000 megabits per fiber per 10 km
- 1000Base-T - 1000 megabits of copper per 100 m
- 1000Base-ZX - 1000 megabits single-mode fiber for 70 km
- 10GBase-LR - 10GE single-mode fiber per 10 km
- 10GBase-ER - 10GE single-mode fiber for 40 km
Of course, there are optical modules for other standards, including 40GE and 100GE. I have listed the main types used in provider networks. Usually in the name or specification it is written, according to what standard this or that module will work. But it is still important to see if this standard supports the equipment port where the module will be installed. For example, 100Base-LX will not start in a switch port that supports only 1000Base-LX. This feature must also be considered.
Using spectral compaction
The optical modules described above transmit a signal mainly at a wavelength of 1310 nm or 1550 nm on two fibers (one for transmission, the other for reception). They have a broadband photodetector (take all) and a laser emitting at a certain wavelength (roughly of course). But it is possible to use wavelength compression. This makes it possible to use a smaller amount of fibers to organize several channels, thereby increasing the throughput of a single fiber.
WDM
Such modules work in pairs, on the one hand, the signal is transmitted at a wavelength of 1310 nm, on the other hand, 1550 nm. This allows instead of two fibers for the organization of one channel to use one. The receiver on such modules remains broadband. Happen both for 1GE, and for 10GE. Below is a photo of a pair of WDM modules with different connectors for connecting patch cords LC and SC.
In most cases, it is preferable to use WDM modules for short distances. Their price is not very big (1 thousand rubles per module versus 500 rubles per ordinary). The reason is that you save the whole fiber, then it will be possible to drive out another similar channel later. Although of course there are other ways to save fiber.
CWDM
Further continuation of WDM technology. With its use you can achieve up to 8 duplex channels on a single fiber. For these purposes, CWDM multiplexers are used (passive devices with a prism inside, allowing to divide the signal according to colors with a step of 20 nm in the range from 1270 nm to 1610 nm). For this, special CWDM modules are also used, commonly called “color” in common people, they transmit a signal at a specific wavelength. At the same time, the receiver on them is broadband. In addition, such optical modules are often made for transmission over long distances (up to 160 km). The figure below shows a small set of CWDM-SFPs, where you can pick up 2GE on a single fiber using multiplexers.
As you can see, the bows are different for everyone. Depending on the wavelength, the module has its own coloring. Unfortunately, they are different for all manufacturers.
Here comes the concept of the optical budget . True, his calculation is beyond the scope of this article. In short, the more ports available, the more channels you can multiplex, the more attenuation there will be. In addition, different wavelengths give different attenuation per kilometer of the transmitted signal. And you need to consider the type of fiber ...
You can write a lot about methods of selecting such modules, about the intersection of wavelengths, about unwanted lengths, about ADD / DROP-modules. But this is a separate issue.
Connectors
This is the place where you will connect the optical patchcord. On the optical modules, two types of connectors are currently being used — SC and LC. Rough and slang - large and small squares. It is clear that having a patchcord with a SC connector, you will not connect it to the LC connector. You need to either change the patchcord, or put the adapter adapter. In most cases, SFP modules have an LC connector, while X2 / XENPAK is a SC. Above, the images already had modules with different connectors.
Little about patch cords
Optical patch cords, they are also optical cords. We will be interested in the following characteristics: duplex / simplex (number of fibers), polishing (now it is UPC-blue or APC-green), connector (SC, LC, FC), multi-mode and length. Of course, the thickness of the fiber core is also important, but now for multimode ordinary cords use the standard thickness. Below, I presented an image with various kinds of patch cords.
Basically you will meet the following designation cords - SHO-2SM-SC / UPC-SC / UPC-3.0 . This is interpreted as follows: Optical Duplex Single Mode Cord (Single-Mode) with SC connectors and UPC polishing on one side and SC-UPC with another length of 3.0 meters. Accordingly, for example, the SHO-SM-LC / APC-SC / APC-15.0 is a single-mode duplex cable with LC-LC connectors and 15 meters long APC engraving.
Basically you will meet the following designation cords - SHO-2SM-SC / UPC-SC / UPC-3.0 . This is interpreted as follows: Optical Duplex Single Mode Cord (Single-Mode) with SC connectors and UPC polishing on one side and SC-UPC with another length of 3.0 meters. Accordingly, for example, the SHO-SM-LC / APC-SC / APC-15.0 is a single-mode duplex cable with LC-LC connectors and 15 meters long APC engraving.
Some features
Optical modules are active equipment; they consume electricity and generate heat. This should be considered when connecting equipment to an electrical outlet. Also, a switch filled with powerful modules to the outset may require additional cooling.
Do not forget that lasers are built into the optical modules, and some safety precautions must be observed with them. Of course, in most cases, they do not provide any threat due to weak power, but there have been cases; long-range, powerful 10GE modules can burn out the retina or leave a burn if you use your finger as an attenuator.
Modern optical modules have the DDM (Digital Diagnostics Monitoring) function - they have a number of sensors built in through which you can determine the current value of some parameters. It looks through the interface of the equipment in which the module is installed. The most important parameters for you are the current received power and temperature.
A number of network equipment manufacturers prohibit the use of third-party modules in their equipment. At least before Cisco did not let them run, they simply did not work in it. Now, in narrow circles, teams are known that open up the possibility of using third-party devices, and Cisco has become less sensitive to this issue. However, if you wish, you can reflash any modules, there are special programmers on sale.
The port on the equipment (in most cases) lights up if a signal of sufficient power arrives at the module. If you connect two two-fiber modules with a single patchcord (just reception with transmission), on the one hand the port will light up, but nothing will work.
Yes, power may not only be weak. If the signal comes too strong, you can burn the photodetector. This usually refers to long-range power modules with a distance of> 80 km. To reduce power use special attenuators. Although if you do in the laboratory, you can simply wind a couple of coils of the patchcord on any pen or pencil.
Finally
Well that's all. The information presented here is enough to not get lost when choosing the module you need. It is important not to forget the main characteristics:
- form factor
- standard (speed)
- spectral compaction and power
- connectors
If someone interested in the topic, I advise you to look at the following:
Source: https://habr.com/ru/post/188224/
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